(1) Field of the Invention
The present invention relates to lithium manganese composite oxides, and in particular relates to the lithium manganese composite oxides used in the positive electrode used for secondary batteries.
(2) Description of the Related Art
Lithium manganese composite oxides are used for the positive electrode of secondary batteries, such as an aqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery. The secondary batteries have been already put in practical use as the power supply for mobile phones, notebook computers, and the like. Furthermore it is attempted to use the secondary batteries also in mid-to-large scale applications, such as automobile applications, electric power storage applications, and the like.
As the lithium manganese composite oxides used in the positive electrode of the conventional secondary batteries, those having a formula Li2-xMn1-yMyO3-Z (wherein M is one or more selected from the group consisting of Fe, Al, Ni, and Co, and 0<x<=0.9, 0<=y<=0.5, 0<Z<=0.9) are disclosed in JP-A-2005-071807 (see the claims, and Paragraph [0018] in the specification). The publication also describes that because, in Li2MnO3, Mn is tetravalent and stable and Li ions are unlikely to be removed and electrochemically stable, Li2MnO3 usually does not exhibit charge and discharge reactions, nevertheless, by depriving oxygen to make the valence of Mn four or less, as in the lithium manganese composite oxides represented by the above-described formula, it is possible to remove Li ions until the valence of Mn becomes four, resulting in exhibiting the reversible charge and discharge reaction.